I suppose it's the same reason there are loads of Linux distros or some people (like me) build their own PC's while it can be cheaper to buy a Dell one.
These people like Windows, they like the software, but they don't like the fact that they cannot control what happens inside Windows.
This way if something breaks, they can fix it and if they want to add a new feature, they can but they don't have to lobby software companies to make a OS compatable Photoshop or Office suite as they can go to a shop and buy it.
And that last point is why I think they don't code to Linux